Define libc_pauthtest to be used in cfg expressions

As the `target_abi` is an experimental feature and can not be used in
`cfg`.

Author: jchlanda

build.rs

@@ -35,6 +35,7 @@ const ALLOWED_CFGS: &[&str] = &[
     // Corresponds to `_REDIR_TIME64` in musl: symbol redirects to __*_time64
     "musl_redir_time64",
     "vxworks_lt_25_09",
+    "libc_pauthtest",
 ];
 
 // Extra values to allow for check-cfg.
@@ -53,7 +54,6 @@ const CHECK_CFG_EXTRA: &[(&str, &[&str])] = &[
         "target_arch",
         &["loongarch64", "mips32r6", "mips64r6", "csky"],
     ),
-    ("target_abi", &["pauthtest"]),
 ];
 
 /// Musl architectures that define `_REDIR_TIME64` (i.e. those that transitioned
@@ -72,6 +72,13 @@ fn main() {
     let target_arch = env::var("CARGO_CFG_TARGET_ARCH").unwrap_or_default();
     let target_abi = env::var("CARGO_CFG_TARGET_ABI").unwrap_or_default();
 
+    // FIXME(msrv): Once the MSRV is 1.78, use `cfg(target_abi = "pauthtest")`
+    // directly instead of translating it to `libc_pauthtest`. `target_abi`
+    // cannot be used directly in cfg expressions on the current MSRV.
+    if target_abi == "pauthtest" {
+        println!("cargo:rustc-cfg=libc_pauthtest");
+    }
+
     // FIXME: this can be removed in 1-2 releases
     println!("cargo:rerun-if-env-changed=RUST_LIBC_UNSTABLE_FREEBSD_VERSION");
     if env::var("RUST_LIBC_UNSTABLE_FREEBSD_VERSION").is_ok() {

src/unix/mod.rs

@@ -519,15 +519,15 @@ cfg_if! {
         #[link(name = "dl", cfg(not(target_feature = "crt-static")))]
         #[link(name = "c", cfg(not(target_feature = "crt-static")))]
         extern "C" {}
-    } else if #[cfg(target_abi = "pauthtest")] {
+    } else if #[cfg(libc_pauthtest)] {
         #[link(name = "c")]
         #[link(name = "m")]
         #[link(name = "rt")]
         #[link(name = "pthread")]
         #[link(name = "dl")]
         extern "C" {}
     } else if #[cfg(any(
-        all(target_env = "musl", not(target_abi = "pauthtest")),
+        all(target_env = "musl", not(libc_pauthtest)),
         target_env = "ohos"
     ))] {
         #[cfg_attr(